We have discovered a novel cytochrome P-450-dependent oxidative deformylation of aldehydes with concomitant introduction of unsaturation into the residual carbon framework [Vaz, Roberts and Coon, J. Am. Chem. Soc. 113 5886-5887 (1991)]. This reaction may be a useful model for the demethylation reactions catalyzed by the steroidogenic cytochrome P-450 enzymes, aromatase and lanosterol-14alphademethylase, where formic acid and an olefinic product are also formed. From our results with oxidants that substitute for molecular oxygen, NADPH, and the reductase in cytochrome P-450-catalyzed reactions, we conclude that an iron oxene, which is the generally accepted form of the active oxidant in P-45 catalyzed reactions, is not the active oxidant in oxidative deformylation. Instead, the results implicate a molecular oxygen-derived, iron-bound peroxide as the active oxidant. A peroxyhemiacetal-like adduct formed from the iron-bound peroxide and the aldehyde is proposed to be an intermediate which undergoes a concerted Beta-scission reaction to yield formic acid and the olefin. A role for 02-derived peroxide in oxidative reactions catalyzed by cytochrome P-450 has not been previously demonstrated. This reaction is a common route to metabolic disposition of aldehydes as demonstrated by the catalytic activity of several purified forms of rabbit cytochrome P-450 and various aldehydes [Roberts, Vaz and Coon, Proc. Natl. Acad. Sci. 1991 in press]. The objectives of this proposal are three fold. To elucidate the mechanism of this novel cytochrome P-450-catalyzed reaction with aldehydes, and determine its relevance to the reactions catalyzed by aromatase and lanosterol-14 alpha-demethylase; to identify the electronic and structural nature of the active oxidant; and, to examine the scope of this reaction as a model for the adrenal progesterone-17,20-lyase P450 and the testis delta-16 C-19 steroid synthesizing P-450 in pig.